Download Genetics IB Syllabus

Essential idea: The structure of DNA allows efficient storage of genetic information.
2.6 Structure of DNA and RNA
Nature of science: Using models as representation of the real world—Crick and Watson used model making to discover the structure of DNA. (1.10)
Understandings:
 The nucleic acids DNA and RNA are polymers of nucleotides.
 DNA differs from RNA in the number of strands present, the base composition
and the type of pentose.
 DNA is a double helix made of two antiparallel strands of nucleotides linked by
hydrogen bonding between complementary base pairs. Applications and skills:
 Application: Crick and Watson’s elucidation of the structure of DNA using model
making.
 Skill: Drawing simple diagrams of the structure of single nucleotides of DNA and
RNA, using circles, pentagons and rectangles to represent phosphates, pentoses
and bases. Guidance:
 In diagrams of DNA structure, the helical shape does not need to be shown, but
the two strands should be shown antiparallel. Adenine should be shown paired
with thymine and guanine with cytosine, but the relative lengths of the purine
and pyrimidine bases do not need to be recalled, nor the numbers of hydrogen
bonds between the base pairs.
International-mindedness:
Theory of knowledge:
The story of the elucidation of the structure of DNA illustrates that cooperation and
collaboration among scientists exists alongside competition between research
groups. To what extent is research in secret ‘anti-scientific’? What is the
relationship between shared and personal knowledge in the natural sciences?
Utilization:
Syllabus and cross-curricular links:
Biology
Topic 2.2 Water
Topic 3.5 Genetic modification and biotechnology
Topic 7 Nucleic acids
Aims:
Essential idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.
2.7 DNA replication, transcription and translation
Nature of science: Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8)
Understandings:
 The replication of DNA is semi-conservative and depends on complementary
base pairing.
 Helicase unwinds the double helix and separates the two strands by breaking
hydrogen bonds.
 DNA polymerase links nucleotides together to form a new strand, using the
pre-existing strand as a template.
 Transcription is the synthesis of mRNA copied from the DNA base sequences
by RNA polymerase.
 Translation is the synthesis of polypeptides on ribosomes.
 The amino acid sequence of polypeptides is determined by mRNA according to
the genetic code.
 Codons of three bases on mRNA correspond to one amino acid in a
polypeptide.
 Translation depends on complementary base pairing between codons on
mRNA and anticodons on tRNA. Applications and skills:
 Application: Use of Taq DNA polymerase to produce multiple copies of DNA
rapidly by the polymerase chain reaction (PCR).
 Application: Production of human insulin in bacteria as an example of the
universality of the genetic code allowing gene transfer between species.
 Skill: Use a table of the genetic code to deduce which codon(s) corresponds to
which amino acid.
 Skill: Analysis of Meselson and Stahl’s results to obtain support for the theory
of semi-conservative replication of DNA.
 Skill: Use a table of mRNA codons and their corresponding amino acids to
deduce the sequence of amino acids coded by a short mRNA strand of known
base sequence.
 Skill: Deducing the DNA base sequence for the mRNA strand. Guidance:
 The different types of DNA polymerase do not need to be distinguished.
International-mindedness:
Theory of Knowledge:
Utilization:
Syllabus and cross-curricular links:
Biology
Topic 3.5 Genetic modification and biotechnology
Topic 7.2 Transcription and gene expression
Topic 7.3 Translation
Aims:
Aim 8: There are ethical implications in altering the genome of an organism in
order to produce proteins for medical use in humans.
Core
Topic 3: Genetics
15 hours
Essential idea: Every living organism inherits a blueprint for life from its parents.
3.1 Genes
Nature of science: Developments in scientific research follow improvements in technology—gene sequencers are used for the sequencing of genes. (1.8)
Understandings:
 A gene is a heritable factor that consists of a length of DNA and influences a specific
characteristic.
 A gene occupies a specific position on a chromosome.
 The various specific forms of a gene are alleles.
 Alleles differ from each other by one or only a few bases.
 New alleles are formed by mutation.
 The genome is the whole of the genetic information of an organism.
 The entire base sequence of human genes was sequenced in the Human Genome Project. Applications and skills:
 Application: The causes of sickle cell anemia, including a base substitution mutation, a change
to the base sequence of mRNA transcribed from it and a change to the sequence of a
polypeptide in hemoglobin.
 Application: Comparison of the number of genes in humans with other species.
 Skill: Use of a database to determine differences in the base sequence of a gene in two species.
Guidance:
 Students should be able to recall one specific base substitution that causes glutamic acid to be
substituted by valine as the sixth amino acid in the hemoglobin polypeptide.
 The number of genes in a species should not be referred to as genome size as this term is used
for the total amount of DNA. At least one plant and one bacterium should be included in the
comparison and at least one species with more genes and one with fewer genes than a human.
 The Genbank® database can be used to search for DNA base sequences. The cytochrome C gene
sequence is available for many different organisms and is of particular interest because of its
use in reclassifying organisms into three domains.
 Deletions, insertions and frame shift mutations do not need to be included.
International-mindedness:
Sequencing of the human genome shows that all humans share
the vast majority of their base sequences but also that there are
many single nucleotide polymorphisms that contribute to human
diversity.
Theory of knowledge:
There is a link between sickle cell anemia and prevalence of
malaria. How can we know whether there is a causal link in such
cases or simply a correlation?
Utilization:
Aims:
Aim 7: The use of a database to compare DNA base
sequences.
Aim 8: Ethics of patenting human genes.
Essential idea: Chromosomes carry genes in a linear sequence that is shared by members of a species.
3.2 Chromosomes
Nature of science:
Developments in research follow improvements in techniques—autoradiography was used to establish the length of DNA molecules in chromosomes. (1.8)
Understandings:
 Prokaryotes have one chromosome consisting of a circular DNA molecule.
 Some prokaryotes also have plasmids but eukaryotes do not.
 Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
 In a eukaryote species there are different chromosomes that carry different genes.
 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles
of those genes.
 Diploid nuclei have pairs of homologous chromosomes.
 Haploid nuclei have one chromosome of each pair.
 The number of chromosomes is a characteristic feature of members of a species.
 A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.
 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine
sex.
Applications and skills:
 Application: Cairns’ technique for measuring the length of DNA molecules by autoradiography.
 Application: Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster,
Homo sapiens and Paris japonica.
 Application: Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis
familiaris, Oryza sativa, Parascaris equorum.
 Application: Use of karyograms to deduce sex and diagnose Down syndrome in humans.
 Skill: Use of databases to identify the locus of a human gene and its polypeptide product.
Guidance:
• The terms karyotype and karyogram have different meanings. Karyotype is a property of a cell—the
number and type of chromosomes present in the nucleus, not a photograph or diagram of them.
• Genome size is the total length of DNA in an organism. The examples of genome and chromosome
number have been selected to allow points of interest to be raised.
• The two DNA molecules formed by DNA replication prior to cell division are considered to be sister
chromatids until the splitting of the centromere at the start of anaphase. After this, they are
individual chromosomes.
International-mindedness:
Sequencing of the rice genome involved cooperation between
biologists in 10 countries.
Theory of Knowledge:
Utilization:
Syllabus and cross-curricular links:
Biology: Topic 1.6 Cell division
Aims:
Aim 6: Staining root tip squashes and microscope
examination ofchromosomes is recommended but not
obligatory.
Aim 7: Use of databases to identify gene loci and protein
products of genes.
Essential idea: Alleles segregate during meiosis allowing new combinations to be formed by the fusion of gametes.
3.3 Meiosis
Nature of science:
Making careful observations—meiosis was discovered by microscope examination of dividing germ-line cells. (1.8)
Understandings:
 One diploid nucleus divides by meiosis to produce four haploid nuclei.
 The halving of the chromosome number allows a sexual life cycle with fusion of gametes.
 DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.
 The early stages of meiosis involve pairing of homologous chromosomes and crossing over
followed by condensation.
 Orientation of pairs of homologous chromosomes prior to separation is random.
 Separation of pairs of homologous chromosomes in the first division of meiosis halves the
chromosome number.
 Crossing over and random orientation promotes genetic variation.
 Fusion of gametes from different parents promotes genetic variation.
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Applications and skills:
Application: Non-disjunction can cause Down syndrome and other chromosome abnormalities.
Application: Studies showing age of parents influences chances of non- disjunction.
Application: Description of methods used to obtain cells for karyotype analysis e.g. chorionic
villus sampling and amniocentesis and the associated risks.
Skill: Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid
cells.
Guidance:
 Preparation of microscope slides showing meiosis is challenging and permanent slides should
be available in case no cells in meiosis are visible in temporary mounts.
 Drawings of the stages of meiosis do not need to include chiasmata.
 The process of chiasmata formation need not be explained.
Theory of Knowledge:
In 1922 the number of chromosomes counted in a human cell was
48. This remained the established number for 30 years, even
though a review of photographic evidence from the time clearly
showed that there were 46. For what reasons do existing beliefs
carry a certain inertia?
International-mindedness:
Utilization:
An understanding of karyotypes has allowed diagnoses to be made
for the purposes of genetic counseling.
Syllabus and cross-curricular links: Biology
Topic 1.6 Cell division
Topic 10.1 Meiosis
Topic 11.4 Sexual reproduction
Aims:
Aim 8: Pre-natal screening for chromosome abnormalities
gives an indication of the sex of the fetus and raises ethical
issues over selective abortion of female fetuses in some
countries
Essential idea: The inheritance of genes follows patterns.
3.4 Inheritance
Nature of science:
Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data. (3.2)
Understandings:
Theory of knowledge:
Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants
Mendel’s theories were not accepted by the scientific
were crossed.
community for a long time. What factors would encourage
• Gametes are haploid so contain only one allele of each gene.
the acceptance of new ideas by the scientific community?
• The two alleles of each gene separate into different haploid daughter nuclei during meiosis.
• Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele
or different alleles.
Utilization:
• Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.
Syllabus and cross-curricular links:
• Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some
Biology
genetic diseases are due to dominant or co-dominant alleles.
Topic 1.6 Cell division
• Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due
to their location on sex chromosomes.
• Many genetic diseases have been identified in humans but most are very rare.
Aims:
• Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and
Aim 8: Social implications of diagnosis of mutations,
cancer.
including the effects on the family and stigmatization.
Applications and skills:
• Application: Inheritance of ABO blood groups.
• Application: Red-green colour blindness and hemophilia as examples of sex- linked inheritance.
• Application: Inheritance of cystic fibrosis and Huntington’s disease.
• Application: Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
• Skill: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
• Skill: Comparison of predicted and actual outcomes of genetic crosses using real data.
• Skill: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
Guidance:
• Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as
Xh.
• The expected notation for ABO blood group alleles is: